https://wiki2.dovecot.org/TestInstallation

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Jul 11 01:03:55 ubuntu-2gb-nyc1-01-mywebserver dovecot: auth: Debug: client in: AUTH#0113#011PLAIN#011service=imap#011secured#011session=kzYhPgBUCpd/AAAB#011lip=127.0.0.1#011rip=127.0.0.1#011lport=143#011rport=38666#011resp=c2Ftd0BteXdlYnNlcnZlci5jb210ZXN0 (previous base64 data may contain sensitive data)
Jul 11 01:03:55 ubuntu-2gb-nyc1-01-mywebserver dovecot: auth-worker(4434): Debug: sql(samw@mywebserver.com,127.0.0.1): query: SELECT email as user, password FROM virtual_users WHERE email='samw@mywebserver.com';
Jul 11 01:03:55 ubuntu-2gb-nyc1-01-mywebserver dovecot: auth-worker(4434): sql(samw@mywebserver.com,127.0.0.1): Password mismatch
Jul 11 01:03:55 ubuntu-2gb-nyc1-01-mywebserver dovecot: auth-worker(4434): Debug: sql(samw@mywebserver.com,127.0.0.1): SHA512-CRYPT(test) != ''
Jul 11 01:03:57 ubuntu-2gb-nyc1-01-mywebserver dovecot: auth: Debug: client passdb out: FAIL#0113#011user=samw@mywebserver.com

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-- non-reversible update
UPDATE virtual_users SET password = ENCRYPT(password, CONCAT('$6$',sha(RAND())))